The European Commission said the detained members of the Association of Poles in Belarus, including Andżelika Borys, Andrzej Poczobut and Irena Biernacka, should be released immediately and unconditionally, Poland's PAP news agency reported.
The EU executive's appeal came after it last month called for two senior members of the Polish minority in Belarus to be immediately released.
The European Commission said at the time that the Belarusian authorities had started targeting the Polish minority in that country, which is Poland's eastern neighbour.
It added, in comments reported by the Polish state news agency, that the Belarusian authorities have been orchestrating campaigns against human rights activists, the opposition and journalists.
Andrzej Poczobut, a senior member of the Association of Poles in Belarus, was detained by police in the city of Grodno, close to the Polish border, on March 25.
Andrzej Poczobut. Photo: PAP/Jakub Kamiński
Meanwhile, Andżelika Borys, the head of the association, was detained by police in Grodno two days earlier.
She was later sentenced to 15 days of confinement for organizing an "illegal mass event" and then charged as part of a criminal investigation into "inciting hatred," according to a report.
Andżelika Borys. Photo: PAP/Leszek Szymański
Stop treating Poles as 'hostages': PM
Poland's Prime Minister Mateusz Morawiecki last month urged the Belarusian authorities not to "harass" Poles in that country and to stop treating them as "hostages."
The prime minister’s chief of staff, Michał Dworczyk, said that the detention of Borys was "a typical example of an attempt to intimidate the Polish community" in Belarus.